The invention concerns a method for separation of chalcogens from waste gases at process installations, as well as a device for separation of chalcogens that form during industrial processes in process installations in the gaseous state.
Sulfur, selenium, tellurium and their chemical compounds with each other or other substances, or their mixtures are generally referred to as chalcogens and have a solid state of aggregation at room temperature around 20° C. The chalcogens can be used as process substances for conversion of metallic layers, so-called precursor layers, for example, on silicon or glass substrates, to a compound semiconductor layer.
Conversion or transformation of metallic precursor layers containing copper/gallium and indium by chalcogens to a compound semiconductor layer ordinarily occurs at high temperatures in a process installation for thermal processes, for example, tempering or muffle furnace. Typical conversion temperatures lie at 500° C. to 600° C. The conversion temperature is then so high that chalcogens present in the solid state of aggregation at room temperature assume a vaporous or gaseous state of aggregation within the process installation.
Chalcogen in excess is generally required for conversion/transformation of the precursor layer to a semiconducting compound semiconductor layer. Part of the vaporous chalcogen reacts with the metal atoms of the precursor layer to a semiconducting compound semiconductor layer. Another part of the chalcogen is released in the gaseous state or as vapor, like selenium vapor, and must be completely removed from the process installation, including the waste gas installations or pipelines, as well as from the waste gases leaving the process installation.
Temperatures from 400° C. to 600° C. generally prevail in process installations for production of semiconducting layers from compound semiconductors that contain copper, gallium, indium and selenium and/or sulfur. Metallic layers, which can contain copper, gallium and indium, are converted at these temperatures together with sulfur, selenium or tellurium, their chemical compounds with each other or with other substances or their mixtures, i.e., the chalcogen, to semiconducting layers. The chalcogen assumes the gaseous state of aggregation under the process conditions, i.e., the stipulated temperature and stipulated pressure and is introduced in excess to the thermal process installation used for conversion.
Part of the chalcogen reacts with the metallic layers to semiconducting compounds in semiconductor layers. Another part of the chalcogen is released in the process installation and must be removed from it. Typically the excess chalcogen, containing selenium, sulfur, tellurium and other substances condenses in or on cooler installation parts—generally at undesired locations—forming fixed deposits there that must be removed with effort from the process installation in the context of maintenance work.
Removal of deposits can occur by opening the process installation and mechanical or chemical removal. However, this is much too costly for industrial processes and therefore not an appropriate means to eliminate deposits, especially since the process in the process installation must be interrupted each time for this purpose.
Long shutdown times in process installations are the result. At the now common installation sizes a few kilograms of sulfur, selenium and/or tellurium are formed typically per process day. These are significant amounts of deposits that adversely affect functioning of the process installation. The deposits must therefore be continuously removed as effectively as possible from the process installation during its continuous operation.
Cooled separation plates for defined deposition of the excess chalcogens in the process installations, like tempering furnaces have thus far been used. These separation plates are arranged here in the gas stream, i.e., in the active part of the tempering furnace, and must be removed from time to time from the processing installation and replaced by clean separation plates. Defined cooling of the separation plates, as well as simple and effective replacement of the plates for maintenance purposes are problems in this case. Maintenance of such an installation part is therefore very time-consuming and laborious and leads to long shutdown times. Apart from this, the chalcogens cannot be completely eliminated from the waste gases in this way.